Ureotelic animals have the ability to produce urea has a nitrogen based compound. The livers of ureotelic animals have the ability to hydrolyse l-arginine and other guanidino compounds.

The chemical reactions involving urea, include the water soluble compound O=C-(NH2)2. The compund is produced in produced in the animal's liver. The process is called the ornithine cycle.

The ornithine cycle is a series of chemical reactions that happen in the liver. Ammonia is changed to urea using ornithine as a carrier.

One group needed comes from the amine group. Another amine group comes from aspartic acid. The aspartic acid is chemically changed to become fumaric acid. It is then changed through transamination into oxaloacetic acid.

Ureotelic animals are animals that excreate nitrogen in the form of urea are called ureotelic. Terrestrial animals have limited supply of water and cannot get rid of ammonia unless it is converted into more compex and less toxic compounds. In ureotelic animals urea is formed in the liver from the nitrogen of amino acids and the excreted by the kidney. But in these animals also some water is required to dissolve urea so that it may be excreted with the urine. Thus, a change from ammonotelic to ureotelic appears to be closely correlated with the supply of water. When the water is plentiful, the tadpole of frog is ammonotelic. But as it metamorphoses and leaves water, it becomes ureotelic.